1. Field of the Invention
Apparatuses and methods consistent with the present general inventive concept relate to an image forming apparatus and method of image forming, and more particularly, to an image forming apparatus and method of image forming which are capable of compensating for a variation in an exposure time, caused by a change in the power of a light source.
2. Description of the Related Art
In general, an image forming apparatus using electrophotography, such as a laser printer, a copy machine, a multi-functional peripheral device, and a facsimile machine, includes an optical scanner. The image forming apparatus prints a desired image by forming an electrostatic latent image on a photosensitive medium by using a light beam output from the optical scanner, and transferring the electrostatic latent image onto paper.
An electrophotographic printer in the related art, such as a color laser printer, includes four photosensitive drums Dy, Dc, Dm, and Dk (not illustrated) prepared to correspond to four colors, e.g., yellow, cyan, magenta, and black, an exposure device that forms an electrostatic latent image of a desired image by scanning light on the photosensitive drums Dy, Dc, Dm, and Dk, a developing device that develops the electrostatic latent image using each of yellow, cyan, magenta, and black developing solutions, and an image forming medium (such as a transfer belt or an intermediate transfer belt) onto which developed images formed on the photosensitive drums Dy, Dc, Dm, and Dk are sequentially transferred to overlap with one another so as to form a complete color image, and via which the complete color image is then transferred onto paper.
Thus, in order to print a desired color image, an image is developed on the four photosensitive drums Dy, Dc, Dm, and Dk by using four colors, e.g., yellow, cyan, magenta, and black, respectively, and the developed images are transferred onto the same location on the image forming medium to overlap with one another so as to obtain a final color image. Then, the final color image is printed on paper.
However, in order to exactly form a desired color image by overlapping four colors on the same location on the image forming medium, all of locations on the respective four photosensitive drums Dy, Dc, Dm, and Dk on which transferring of images onto the image forming medium starts and ends should be the same for these four colors. This is because even if all of the images are clearly developed on the four photosensitive drums Dy, Dc, Dm, and Dk, a final color image obtained when locations on the image forming medium onto which these images are transferred do not coincide to even a small degree does not exactly exhibit the desired colors and image.
Thus, in order to exactly form a color image, it is important to precisely equalize points of time when the four photosensitive drums Dy, Dc, Dm, and Dk start to be exposed using the exposure device, in consideration of a time of driving the image forming medium. A process of equalizing such exposure start times such that a plurality of colors that are to be used to form one image exactly overlap with one another as described above is referred to as color registration.
However, conventionally, since a predetermined exposure start time is used even when the power of the light changes, a plurality of colors may not exactly overlap with one another even after color registration is performed.
Specifically, exposure start times of the respective photosensitive drums are determined based on a falling or rising edge of a horizontal synchronization signal. However, since a change in the power of the light may cause a change in the horizontal synchronization signal, a plurality of colors do not exactly overlap with one another when the rising or falling edge of the horizontal synchronization signal changes due to a change in the power of the light.